1. Field of the Invention
The present invention relates to magnetic recording apparatuses, particularly magnetic disk apparatuses and magnetic heads.
2. Description of the Related Prior Art
Magnetic disk apparatuses are classified into a longitudinal magnetic recording system and a perpendicular magnetic recording system, according to the direction of magnetization of a magnetic film. The perpendicular magnetic recording system can easily realize higher recording density than the longitudinal magnetic recording system, and are expected to be put to practical use in the future. An example of such magnetic heads is seen, for example, in the Journal of Magnetic Society of Japan, Vol. 19,Supplement No. S2,pp. 122–125. Further, time dependency of recorded magnetization in such magnetic recording films and effects of external magnetic field on the characteristics are described in, for example, IEEE Transaction on Magnetics Vol. 35,NO. 5,pp. 2652 (1999) “Activation Volume and Correlation of Media Noise In High-Density Longitudinal Recording Media” or IEEE Transaction on Magnetics Vol. 35,No. 5,pp. 2655 (1999) “Rigid Disk Medium for 20 Gb/in2 Recording Demonstration”.
In both perpendicular magnetic recording and longitudinal magnetic recording systems mentioned above, magnetic heads having the same basic structures are used. A representative example of them will be described below referring to the part pertaining to the present invention.
A general view of a rotary actuator with a magnetic head mounted thereon is shown in FIG. 1, and an enlarged view of the magnetic head 1 is shown in FIG. 2. FIG. 2 is a plan view as seen from above of the magnetic head 1. For positioning of the magnetic head 1 in a magnetic disk apparatus, the rotary actuator 2 is used. The angle formed by the rotating direction (circumferential direction) 4 of the magnetic disk 3 and the thickness direction 91 of magnetic pole is defined as skew angle S. In the magnetic disk apparatus having the rotary actuator 2, the skew angle varies according to the head position in the radial direction. Ordinarily, the skew angle S varies in the range of about 20 degrees, according to the radial head position.
As shown in FIG. 2, the magnetic head 1 comprises a first magnetic pole 15, a recording magnetic pole 8 as a second magnetic pole, and a reproducing head portion 6. The example shown in the figure is an example of ring head. The recording magnetic pole 8 has a film thickness 9 of the magnetic pole and a write track width 7. In the case of a recording and reproducing head such as this example, a reproducing head 6 is disposed in stack with the recording head. Layout of a signal processing system and the like will be described later. In the following figures, the rotating direction (circumferential direction) of the magnetic disk is denoted by symbol 4, and the skew angle is denoted by symbol S.
Attendant on the increase in the density of tracks in magnetic storage devices, the track width of magnetic heads has been made smaller and smaller. As the track width 7 of the recording head is reduced, it becomes difficult for a magnetic flux generated in the head to pass through the recording magnetic pole. Therefore, the recording magnetic pole of the head tends to be saturated easily, and leakage flux to the recording medium is reduced. Accordingly, in the case of recording information on a recording medium by use of a recording head having a small track width, it is required to enlarge the magnetic pole thickness 8 of the recording head or to enhance the saturation flux density of the magnetic pole material for the recording head, in order to generate a sufficient magnetic field from the recording magnetic pole.